Their study examined the reported incidence of invasive breast cancer in regions where the screening programme was implemented in Norway, and compared it with incidences in other regions. The study involved 40,000 women aged 50-69 covering 1996 to 2005.

When the number of cases of breast cancer found in screened women was compared with that in matched unscreened women, the researchers estimated that 15% to 25% more cases of breast cancer were detected that would not have become significant during the women's life spans.

Study leader Dr Mette Kalager, researcher at Harvard Medical School, Boston, said the study showed a ‘substantial ethical and clinical dilemma' over whether screening programmes should exist. ‘This dilemma can be reduced only when potentially fatal cancer that requires early treatment can be reliably identified,' said Dr Kalager.

Last autumn the Government launched an independent review of breast cancer screening policy following research that showed the NHS programme might be doing patients more harm than good.